Electrodynamic painting system and method
AssigneeCaterpillar Tractor Co.
InventorsRobert G. Smead, Thomas J. Richards, Charles E. Lanchantin, Jr.
Life of this patent
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Abstract
An electrodynamic spray painting system having a spray gun (13) for spraying paint toward a workpiece (15) and an electrode (16) for causing a charge to be imposed on the paint. A high voltage waveform generator (21) supplies an oscillating voltage to said electrode (16) such that coronas of varying strengths are periodically, controllably generated. This oscillating voltage enhances the spectrum of charges on the paint particles improving evenness of coverage of paint on the workpiece (15). Additionally, wastage of paint is decreased. This invention is also applicable to other coating materials, such as powders.
Claims29
In an electrodynamic coating apparatus (10) for coating a workpiece (15) with a coating material, said apparatus (10) having first means (13) for propelling a plurality of atomized particles of said coating material through space in a preselected spray pattern (26), said first means (13) having a gun body (30) and a nozzle (24) connected to the gun body (30), the improvement comprising:
- a second means (16,34) including an electrically chargeable electrode (16) for establishing an electric field intermediate the nozzle (24) and the electrode (16) for imparting an initial electrical charge of one polarity to the plurality of atomized particles at the nozzle (24), and for establishing, in response to the electrode (16) being charged to a sufficiently great first level, a zone of ions of an opposite polarity to said one polarity in the pathway of at least a portion of the preselected spray pattern (26), said zone of ions being adapted to neutralize and reverse the polarity of a portion of the charged particles yielding a plurality of diversely charged particles;
- and,
- third means (21) for continuously varying the charge applied to said electrode (16) over a range that includes said first level and a second level of a magnitude insufficient for maintaining said zone of ions.
An electrodynamic coating apparatus (10) for coating a workpiece (15) with a coating material, said apparatus comprising:
- first means (13) for propelling a plurality of atomized particles of said coating material through space in a preselected spray pattern (26), said first means (13) having a gun body (30) and a nozzle (24) connected to the gun body (30);
- and,
- second means (16,21,34), including an electrode (16), for imparting an initial electric charge to a plurality of said atomized particles
- and for establishing a varying electric field between the nozzle (24) and the electrode (16), said second means (16,21,34) including a high voltage waveform generator (21) having a discharge circuit (43) and a D.C. high voltage power supply (34) having an output grounded through a discharge circuit (43), said discharge circuit (43) including a capacitor (38) and an air gap (42) in parallel, and having a second resistor (40) in parallel with said capacitor (38) and in series with said air gap (42).
In an electrodynamic coating apparatus (10) for coating a workpiece (15) with a coating material, said apparatus having first means (13) for propelling a plurality of atomized particles of said coating material through space in a preselected spray pattern (26), said first means (13) having a gun body (30) and a nozzle (24) connected to the gun body (30), the improvement comprising:
- second means (16,34) including an electrically chargeable electrode (16) for establishing an electric field intermediate the nozzle (24) and the electrode (16) for imparting an initial electrical charge of one polarity to the plurality of atomized particles at the nozzle (24), and for establishing, in response to the electrode (16) being charged to a sufficiently great first level, a zone of ions of an opposite polarity to said one polarity in the pathway of at least a portion of the preselected spray pattern (26), said zone of ions being adapted to neutralize and reverse the polarity of a portion of the charged particles yielding a plurality of diversely charged particles;
- and,
- power supply means (22) for establishing a charge of varying magnitude on the workpiece (15), said power supply means (22) being in electrical contact with said workpiece (15).
A method for coating a workpiece (15) with a coating material, comprising the steps of:
- establishing a cyclically varying first electric field proximate a spary nozzle (24), said spray nozzle (24) being adapted to accept a surface charge, said surface charge being of a strength and polarity dependent upon said electric field;
- spraying said coating material from said nozzle (24) toward said workpiece (15);
- and
- creating a periodic corona in the path of at least a portion of said coating material.
An electrodynamic coating apparatus (10) for coating a workpiece (15) with a coating material, comprising:
- first means (13) for propelling a plurality of atomized particles of said coating material through space in a preselected spray pattern (26);
- second means (16,34) for establishing an electric field positioned such that at least a portion of said spray pattern (26) passes through said electric field, said second means (16,34) being adapted for cooperating with said first means (13) for imparting an initial electric charge to a plurality of said atomized particles at the origin of said spray pattern (26);
- and,
- third means (21,43) for continuously varying the strength of the electric field such that a corona is repeatedly created and destroyed at a position at least partially located within the space occupied by said spray pattern (26).
The electrodynamic coating apparatus (10), as set forth in clam 16, wherein said nozzle (24) is electrically conductive and is grounded.
A method of electrostatically coating a workpiece (15) with a liquid paint, comprising:
- projecting the paint from a gun nozzle (24) of a gun (30) in a plurality of atomized particles in a preselected spray pattern (26), said gun (30) having an electrode (16) insulated therefrom and so spaced from the nozzle (24) and so shaped as to be capable of generating a corona discharge in its vicinity when adequately charged;
- establishing a recurring first condition in which a first electric field exists between the electrode (16) and the nozzle (24), said electric field being sufficient for both imparting an initial electric charge of one polarity to the plurality of atomized paint particles at the nozzle (24) and for generating a corona discharge;
- and
- establishing during said first condition a zone of ions in said corona discharge at the electrode (16) in the pathway of the preselected spray pattern (16) sufficient for thereafter neutralizing and reversing the polarity of a portion of the charged particles emanating from said nozzle (24) and providing a plurality of diversely charged particles;
- establishing a recurring second condition in which a second electric field exists between the electrode (16) and the nozzle (24), said second electric field being free from being sufficient for generating a corona discharge in the pathway of the preselected spray pattern (16);
- alternating between said first and second conditions;
- and
- electrically charging said workpiece (15).
Dependencies are inferred from the claim text.